In very tall buildings it is not generally possible to profitably construct elevator hoistways that extend from the base floor up to the top floors of the building, the elevators operating in which hoistways would serve all the floors of a building. For this reason the floors of high-rise buildings are conventionally divided into floor zones, which are served with their own local elevators. To arrange the traffic between the zones, some of the floors function as so-called transfer levels (transfer floors), between which shuttle elevators operate taking passengers from the entrance lobby of the building to transfer floors and vice versa. When arriving at a transfer floor according to the route, a passenger takes a local elevator for traveling to the final destination floor. Prior-art solutions, in which local elevators move in their own elevator hoistways, are disadvantageous from the viewpoint of space usage, however, because the number of elevator hoistways needed becomes large. One known method to improve space usage is to dispose a number of elevator cars in the same elevator hoistway. U.S. Pat. No. 5,419,414, among others, discloses an elevator system in which three elevator cars are installed into the same elevator hoistway such that each elevator car is controlled by means of elevator machines disposed in a machine room at the top end of the elevator hoistway. Elevator ropes pass in an overlapping manner from the elevator machines to the elevator cars such that the elevator ropes going to the lowermost elevator car pass two other elevator cars and the elevator ropes going to the middle elevator car pass the topmost car. Corresponding overlapping must be made for the roping of the counterweights of the elevator cars. The cars can drive in the same elevator hoistway in relation to each other according to, among others, the following principles:                each elevator car moves in its own part of the elevator hoistway, i.e. in a zone, and they do not thus go into the hoistway area of another elevator,        all the elevator cars can serve all the floors but only one elevator car moves at a time,        the elevator cars can move at the same time but only in the same direction,        the elevator cars can move in different directions so long as passenger safety is guaranteed, e.g. the two lowermost cars can move downwards and the topmost car upwards.        
U.S. Pat. No. 6,871,727 discloses an elevator system, in which two-car elevators are used as shuttle elevators, which operate between transfer levels. The local elevators operating in different zones are arranged in the same elevator hoistway such that a passenger can transfer from a lower transfer floor of a transfer level to local elevators with which the passenger can get to floors lower than the transfer level, while from an upper transfer floor of a transfer level a passenger can get to local elevators that run to floors higher than the transfer level. By disposing local elevators in the same elevator hoistway, the number of elevator hoistways can be considerably decreased and thus also the space needed for elevator hoistways is also reduced. In the solutions presented, a top clearance is arranged for the local elevators, in which the elevator machine of each local elevator is disposed and that being the case the local elevators cannot serve shared floors such as e.g. the floors of a transfer level. The solution in question easily results in underutilization of the transport capacity of the local elevators and also hampers the transfer of passengers from the shuttle elevators to local elevators serving onward connections. Escalators between the transfer floors are also needed for the transfer levels, taking up extra space and making the overall solution expensive and complex.